This invention relates generally to capillary electrophoretic devices. More particularly, it relates to monolithic ionic liquid-channel capillary electrophoretic devices (ILC-CED) and methods of making the same.
Conventional capillary electrophoretic (CE) devices exist for detecting ionic species in liquids. Generally, CE devices separate various ionic species in a liquid sample into separate, discrete detectable zones, wherein each zone corresponds to a single ionic species. This separation is facilitated by an electric field which pulls ions through a capillary. The migration velocity with which the ions travel through the capillary depends on the electrophoretic mobility characteristics of the particular ionic species. Thus, different ionic species travel at different speeds, and separate into discrete zones after a certain time.
A typical CE device consists of a relatively long capillary, e.g., 60 cm in length, having each end immersed in a reservoir containing a buffer solution. A high voltage power source is coupled to the tube and a detector can be coupled at either end of the tube to detect the changes in potential caused by the passage of various ionic species. A sample containing different species is introduced into the device at one end by either hydrostatic force or electromigration. The ionic species present in the sample migrate through the tube under an applied electric potential created by the voltage source. The buffer solution, usually an electrolyte, provides a source of ions for the system and facilitates movement of the ionic species through the tube by providing a background, or transportation, medium through which the species travel. The ions are detected by a light absorbing detector located near the output of the tube. Other conventional devices employ gels, such as polyacrylamide gels, instead of a liquid analyte as a background medium.
A drawback of the conventional CE devices is the high voltages necessary to move the ionic species through the capillary. Typically, the electric field created by the voltage source moves the ionic species through the tube at migration velocities sufficient to separate the species into discrete detectable zones. However, relatively high voltages, usually on the order of 10 kV to 30 kV, are required to generate this ion-separating potential. These elevated voltage levels typically necessitate shielding of the voltage source. Thus, the CE device is relatively large.
Another drawback of conventional CE devices is the relatively long capillaries that are employed. These relatively long capillaries increase the time it takes to detect selected ions that are migrating through the tube, since the ions must travel greater distances before they separate into discrete zones.
Still another drawback of conventional CE devices are the mechanical parts that are necessary to insure proper operation of the device. For example, conventional CE devices, because of their relatively long length, require a fan to circulate air around the capillary to help dissipate heat to the ambient environment. Further, the conventional CE device requires light sources and detectors to detect the ionic species present in the sample solution.
There still exists a need in the art for better electrophoretic devices that can separate ionic species into discrete detectable zones while using relatively small external voltages, and relatively small capillary tubes. In particular, a CE device that relatively easily and relatively quickly determines various ionic constituents in a liquid sample, while decreasing size and increasing sensitivity, would represent a major improvement in the art. Additionally, an electrophoretic device that is relatively easy to manufacture would also present a major improvement in the art. Moreover, a device that can be adapted for use in a relatively low cost hand-held instrument would likewise present an improvement in the art.